68 OUTLINES OF EVOLUTIONARY BIOLOGY 



results both for pure biology and for medical science, owes its 

 origin and development entirely to the elaboration of the cell 



FIG. 29. Part of the Plasraodiura of a Mycetozoon (Budhamia utricularis], 



X 50. (From a photograph.) 

 The small dark spots are the very numerous nuclei. 



theory under the influence of improved methods of microscopical 

 investigation. 



There is another point of view with regard to the living cell 

 which we may briefly refer to in this place. It is not only the 

 morphological or structural unit of the body but also the physio- 

 logical or functional unit. All the essential vital processes take 

 place within the bodies of cells, and all the different materials 

 required for and produced by these processes pass in and out of 

 them. Each cell may be looked upon as a microscopic laboratory 

 in which the complex chemical reactions comprised under the 

 term metabolism take place, and although, in the higher 

 organisms, the cells have become mutually dependent upon one 

 another, yet each retains a certain degree of physiological as 

 well as of morphological individuality. 



